The firing process is one of the most crucial steps in the overall manufacturing operation, so when the company was looking to expand its manufacturing capacity two years ago, it gave special consideration to searching for a new kiln. After evaluating several different options, Du-Co decided to replace its two older tunnel kilns with a custom-designed, fiber-lined tunnel kiln from Swindell Dressler. “We talked to several different kiln manufacturers, but we liked Swindell Dressler’s design best. Additionally, they’re well known in the industry for the quality of their kilns,” says Mike Crytzer, process engineer.
Working closely with Du-Co, Swindell Dressler custom-designed a kiln specifically to meet those needs. The new kiln, which was installed in November 2001, increased the company’s firing capacity by 66% in a fast firing cycle. Even with the greater firing speed, the kiln was designed to ensure that the parts emerging from the exit end are cool to the touch. Recirculating fans were installed in the preheat zone to aid movement of heat throughout the load. Another set of recirculating fans is located in the ware cool zone. These fans, in conjunction with exit end air nozzles, help to shape the cooling curve. Excess heat from this zone is recycled into a dryer. By the time the cars cycle to the unloading section, the ware is cool enough to be touched with a bare hand, enabling workers to quickly put the products into their final packaging.
A Honeywell UMC800 controls the kiln’s temperatures by monitoring the roof thermocouples and adjusting the zone actuators accordingly. A disk in the UMC800 records several trends, including temperatures and zone outputs. A thermocouple car was built and a Datapaq real-time temperature recording package was included. This system is used to determine the temperatures that the ware is seeing. It also enables the kiln operator to review the temperature uniformity across the load.
“The fact that there’s more uniformity across the kiln car load means that we can schedule parts more easily. With our old kilns, we had to fire our products in different layers depending on the temperature in each section of the kiln. Now we can just throw parts into the kiln without dividing them into top, middle and bottom categories. That’s made our firing process more efficient,” says Crytzer.
The kiln’s increased speed and uniformity, along with other design features, help ensure that the binder is completely burned out during firing. Additionally, the kiln can be shut down as needed without adversely affecting its operation. “The whole plant pretty much runs on a five-day schedule,” says Crytzer. “If we need the extra capacity, we leave the kiln running over the weekend, but if we don’t, we can turn it off. The old kilns had to run all the time, whether we had product to fire or not, and they pretty much dictated our production. With the new kiln, we have more flexibility.”
Ceramic parts—most measuring less than 31⁄2 in. in diameter—are loaded into saggers for ease of handling, and kiln cars loaded with saggers are automatically pushed through the system. A touch screen on the car moving control panel makes changing push rates a very simple task. The current push rate is one car every 15 minutes.
The kiln also uses a closed loop for car handling. By using a turntable and an elevator system on both ends, the cars are repositioned and lowered for easier loading and unloading. All work is performed on one side of the kiln cars, further reducing safety hazards.
“We were able to design an automated system that removed the plant personnel from the task of moving kiln cars around, while at the same time simplifying how the automated system is controlled,” explains Ken Meyer, staff engineer for Swindell Dressler.
The higher elevation of the cars while in the kiln allows for the natural draft of the building to maintain a comfortable temperature for employees in the nearby areas.
For more information about tunnel kilns for advanced ceramic components, contact Swindell Dressler Co., P.O. Box 15541, Pittsburgh, PA 15108; (412) 788-7100; fax (412) 788-7110; e-mail email@example.com; or visit http://www.swindelldressler.com.